Laboratory Studies

No specific laboratory tests exist for determining the diagnosis of tetanus. The diagnosis is clinically based on the presence of trismus, dysphagia, generalized muscular rigidity, spasm, or combinations thereof. Although the laboratory findings are not diagnostically valuable, they may help exclude strychnine poisoning.

An assay for antitoxin levels is not readily available. However, a serum antitoxin level of 0.01 IU/mL or higher is generally considered protective, making the diagnosis of tetanus less likely (though rare cases have been reported to occur despite the presence of protective antitoxin levels).

Wounds should be cultured in cases of suspected tetanus. It must be kept in mind, however, that C tetani sometimes can be cultured from the wounds of patients who do not have tetanus and frequently cannot be cultured from the wounds of patients who do.

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Spatula Test

The spatula test is a simple diagnostic bedside test that involves touching the oropharynx with a spatula or tongue blade. In normal circumstances, it elicits a gag reflex, and the patient tries to expel the spatula (ie, a negative test result). If tetanus is present, patients develop a reflex spasm of the masseters and bite the spatula (ie, a positive test result).

In 400 patients, this test had a sensitivity of 94% and a specificity of 100%.
[17] No adverse sequelae (eg, laryngeal spasm) were reported.

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Other Studies

Electromyography (EMG) may show continuous discharge of motor subunits and shortening or absence of the silent interval normally observed after an action potential.

Robert W Tolan Jr, MD Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine